1. Field of the Invention
The present invention relates to a process for producing an electronic device, specifically to a process for producing a substrate for liquid crystal display device or a recording head, comprising removal of a part of the substrate.
2. Related Background Art
Conventionally, in formation of a silicon nitride film on an element side only of a substrate, as shown in FIG. 10, silicon nitride films 12,13 are once formed by CVD (Chemical Vapor Deposition) on both faces of substrate 11 inevitably owing to the CVD apparatus constitution, and thereafter silicon nitride film 13 from the reverse face is removed.
In one method for the above film formation on one face side, photoresist 16 or the like is applied on silicon nitride film 12, and silicon nitride film 13 on the reverse face is removed by etching. A hot phosphoric acid solution is a general etchant for silicon nitride. However, photoresist 16 is not sufficiently resistant against the hot phosphoric acid, so that this wet etching is not applicable for the silicon nitride film removal.
Therefore, the removal of the silicon nitride film on the reverse face is usually conducted by dry etching for formation of a silicon nitride film only on the element side face.
The dry etching method includes CDE (chemical dry etching), RIE (reactive ion etching), and so forth. In the CDE method, one of the faces should be protected by protection film such as a photoresist to prevent etching of both of the front face and the reverse face by the diffused gas. In the RIE method, the substrate should be turned over before the etching of the nitride film on the reverse face, since only the face exposed to plasma is etched in usual RIE system. For the turning-over, the front face (element side) of the substrate is brought into contact with an arm, a belt or the like or the electrode of the apparatus. This can cause scratches on the element face, or dust formation to give defects of the element. To prevent the defects, the surface should be protected by a protection film composed of a resin or the like in the RIE method also.
For removing the silicon nitride film on the reverse face of the substrate, the front face (element side) thereof should be protected by forming an organic film like a resist for delivery and etching in any of dry etching methods as described above.
However, disadvantageously the organic resin film will form particles by contact with mechanical parts such as an arm and a belt of the delivery system, or the organic resin will adhere onto the electrode of the apparatus by clamping of the substrate by the electrode to impair the contact of the substrate with the electrode, causing rise of the substrate temperature during etching and impairing the etching selectivity.